Remote-control system for direct current welding



Nov. 3, 1953 c, A, WELCH 2,658,132

REMOTE-CONTROL SYSTEM FOR DIRECT CURRENT WELDING Filed Jan. 6, 1950 2 Sheets-Sheet l A TMR/V573.

c. A. WELCH 2,658,132

REMOTE-CONTROL SYSTEM FOR DIRECT CURRENT WELDING Nov. 3, 1953 2 Sheets-Sheet 2 Filed Jan. 6, 1950 rrrr ' INVENTO @uw a, w

BY Ua-o16 M?, #um

Patented Nov. 3, 1953 STES r"ortica &132

REMOTE-CONTROL SYSTEM FOR DIRECT CURRENT WELDING Application January 6, 1950, Serial No. 137,215

Claims.

This invention relates to direct current welding and particularly concerns a welding system which permits the operator to exercise remote control over the volt-ampere characteristics of a direct current welding generator from the handle of the electrode holder at the site of the Work even though the welding generator furnishing the energy for welding may be at a remote point.

In commercial D. C. Welding practice, it is usually necessary to utilize an alternating current energy source to supply D. C. components to the field Winding of a direct current Welding generator. Consequently, D. C. welding control systems of this type must provide means for rectifying the A. C. source energy so that only D. C. components are applied to the field of the D. C. generator as well as means for controlling the magnitude of the rectied A. C. current applied to the generator and consequently the output of the generator. Moreover, for maximum operating efficiency, it is 'highly desirable to provide built-in remote control means in the handle of the electrode holder so that the operator may conveniently adjust the generator output without interrupting his Work.

Heretofore, a number of systems have been proposed which are intended to permit the operator to exercise remote control over the output characteristics of a D. C. Welding generator, but none have proved to be suiciently rugged or practical for prolonged successful commercial operation. For example, in the past, systems of this type have included utilized fragile grid-controlled, mercury vapor rectiers or so called thyratron tubes. These systems are undesirable because the tubes have to be preheated before they can be operated, require power for lament energizing current, and are too delicate to withstand the rough usage to which they are subjected to in the shop or eld. Other systems have proposed control of the D. C. generator output by complex electromechanical devices Which insert or withdraw resistance from the supply circuit to the generator eld winding. The very nature of such equipment makes it too impractical or costly for commercial utilization. As a consequence, prior remote control systems intended to enable the operator to conveniently adjust the output characteristics at the electrodes from the electrode holder have not achieved commercial acceptance despite the obvious utility of such systems.

The object of the present invention is the provision of an electrical control circuit of simple, inexpensive, durable construction including a primary control device which is adapted to be built into the handle of a Welding electrode holder and Which is effective to enable an operator conveniently to control the volt-ampere characteristics of the D. C. generator. In accordance with this invention, the handle control means dominates the electrical control circuit Which in turn governs the operation of the welding generator.

The voltage and amperage output of a direct current generator may be varied conveniently by adjustment of the excitation of the field winding of the generator, as is well known by those skilled in the art. This invention is predicated upon the principle of rectifying alternating current to a pulsating direct current to provide the energy for exciting the field Winding of the Welding generator, and modifying the magnitude of the excitation energy by the use of a saturable reactor in which the degree of saturation is controlled conveniently from a variable resistance or potentiometer. More specifically, the eld Winding of the generator is coupled, directly or indirectly, with the output terminals of a rectifier which is fed with alternating current through a saturable reactor and the saturable reactor is provided with a control Winding constituting part of a control circuit which includes a variable resistance adapted to be adjusted manually by the operator at the site of Welding. The significance of this arrangement is that it provides practical means for'the remote control of a direct current Welding generator set, and it enables low control voltages to be employed in conjunction With equipment of a rugged and durable nature, The variable resistance need be only a unit of relatively small size and, therefore, it may be installed in or attached to the handle of a Welding electrode Where the operator readily may reach its control knob to adjust the Welding generator output voltage and amperage characteristics without leaving the site of his Work. Moreover, the relatively low voltages which prevail in the control circuit do not require special precautions in respect to insulation, and the leads to the variable resistance or potentiometer in the welding electrode holder may be associated directly with the generator output leads which carry the heavy Welding currents to the electrode.

In the practice of the invention, the saturable reactor may be housed Within a box adapted for association with or direct attachment to the physical Welding generator equipment, and the control circuit, which includes the variable resistance and saturable control winding of the reactor, may be energized from a separate rectifier having its input in connection with the alternating current supply to the machine, or the control circuit may be energized from `any other suitable source.

In one typical embodiment of the invention,` the main windings of the saturable reactor carry alternating current which is impressed upon the input terminals of the exciter rectier, and in this arrangement an adjustment of the control resistance in the control circuit varies the degree of saturation of the rectier, which, in turn, effects the reactor impedance and thereby adjusts the alternating current which is impressed upon the exciter rectier. In a modified form of structure, energy for excitation of the Welding generawhich furnishes exciting energy to it lthrough' uni-directional half-wave rectiiiers. This Yarrangement, though somewhat more immensi-ue than the first one, provides :advantagesiin elimimating the effects of residual magnetism *in the reactor core, and, of course, .is ,particularly adapted for use in conjunction with welding generators which are equipped with separate field exciters. As a further alternative, the saturable reactor output :may .he arranged .for .,fulhwave .rectiieation ythrough halt-Wave rectiers in .a control circuit lof the type rrst described.

Itis also the concept .of this invention .to provide remote control means which valso `can be located -in -the handle -of the-electrode holder for conveniently v4starting andstopping the generator .drive .motor :and eiiecting :reversal of .polar-ity at .the welding electrodes. rIfhis =is 4.accomplished :through .separatecircuits which 'control .a .polarity reversing .switch and .a motor .start-stop switch respectively. These circuits 'are .energized .from

wthe low-'voltage supply circuit to Ythe generator field winding vand consequently .achieve a .maximum economy A.of operation. Moreover, they -are :so .arranged inY conjunction with the leads -of the generator control circuit that Athey .may be -bound Awith `the welding 4cable and the number of leads .-in .thecontrol unit to the .electrode holder reduced to a bare minimum.

lOther objects and advantages .of :this invention will be apparent to those skilled .in the ar-t Afrom the Vfollowing description .of .the drawings .in

which: Y

Figure l is .a top plan View .of a typical electrode holder ,including the remote .control attachment for the .circuit ofzthis invention.

Figure 2 is `acrosssectional viewof the holder attachment taken .along lines 2 2 of .Figure .1.

.Figure 3 is a diagrammatic flattened view of the curved inside surface .of the .electrode holder handle yshowing the polari-ty reversing .and .startstop switches.

Figure 4 is afragmentary view ofthe cable and of the electrode handle showing the control .attachment with the polarity reversing switch in open position.

Figure ,5 is `a View similar toFigure 4 butshowing `the polarity .reversing switch in closed :position.

Figure e a cross sectional .view Ataken along line E-- `of -Figure 2.

Figure i7 .is .a diagrammatic view of fa .circuit embodying .the preferred form .of this invention.

Figure .8 Ais a .diagrammatic yiew showings. .cir- `cuit embody-ing another iormfof this invention.

A preferred form fof rcontrol circuit :embodying this invention @is shown in Figure Thecircuit which is lenergized vfrom .leads :l il from :a conven- .ient source .of :alternating current such :as a three phase 60 cycle source, is adapted to control .the 'volt-ampere characteristics of aD. C. welding generator Il which `is driven by a generator drive motor I2 and supplies -current to welding electrodes i3 and flfll. The power lines IU include protective fuses i5, a main switch i6, Vand lead through a'motor star-ter contactor l1 to the drive motor l2. The -above units `are well'knownin 'the art and do not constitute a part of the present invention.

vThe field I8 of the generator H is D. C. 'excited and the control 'circuit lof this invention Aeffects .25J lof `va transformer 2|.

the vgenerator :output .by control Aof this field. Power for the generator eld voltage is supplied lthrough lines I9 connected across a single phase of the source lines I0 and leading to the primary Secondary 22 of the transformer is connected across the A. C. termi- .;nalsiof .arreotifrer -23 which is preferably of the metallic disk type fby means of connecting leads 24 .and .25. rectifier is introduced in the circuit .for .the purpose of transforming the A. C. 'source energy l'into rectified A. C. (hereinafter :called 13.0.) input for the excitation of the D. C. generator eld winding. Control of the A. C. .supply vto .the rectier 23 .and consequently Athe D. .C. output .of the Arectifier achieved 'by .means vof .a three-.legged saturaljle .reactor .2.5.

.The .center leg of the .saturable .reactor fis wrapped with a coil '3.0 .carrying D. C. current ,supplied from an auxiliary Yc'ircu'it which will hereinafter be described. .Line carrying A. C. current is coiled fin series connection about the .outside .legs .of 'the reactor. Those skilled in the .art will appreciate that lthe A. C. output of lines .2B and 125 is controlled .by the characteristics of .the D. C'. ,passing through the center Icoil Sil, .increasing as 'the D. C.. current is raised and 'decreasing as the D. C'. current is lowered. The

LD. C.. .current passing through coil 30 tends to .saturate the reactor with a resultant reduction in fthe .lmpedance of .the A. -C. circuit which line '25 is .a part. Consequently, the D. C. current is increased through coil 30, the core of the reactor approaches saturation, the impedance is reduced and theA. C. `'current through line 25 increases. Conyersely, .as 'the magnitude of the D. C. decreases, .impedance .increases -and the value of A. C. current in .line .25 drops. The A. C. .current components, since `they change direction rapidly. have. no effect .on the saturation of the core.

'The D. C. output of rectiiier 23 'is taken from the D. C. terminals and 'fed through leads El `and 32 to the bran-ch contacts 33 'and i313 of a polarity reversing switch .35. The opposite 'contacts 13B and 1.3i' ci 'the switch .are connected to Alines S and 39 which lead to the terminals of the Lgenerator held coil i8. Thus, the voltampere .characteristics of the D. C. field coil of the generator and consequently the .generator output are controlled by the strength of the D. C. current supplied to the coil 30 of the .saturablereacton The auxiliary circuit which permits remote control of the generator field from the electrode holder handle comprises lead lines ll and 2 'taken from the source 'lines l@ and connected across the primary of a transformer 43. `When the Amain switch It is closed, 'the primary of the transformer E3 is energized and the loutput voltis reduced through the secondary to permit it to be used vas a control voltage and to supply the input to a rectifier '112 Vwhich is also vof the metallic disk type. This 'rectifier supplies D. C. .current 'through leads .45 and IIB to the ycoil -39 of the saturable reactor, and .is controlled by an adtustablefpotentiometer lil, `eormected in series with leads '45 and '4B and located in the handle of the electrode holder. Adjustment of the po ten'tiometer results in variation .of the resistance Aof the circuit 'from the D. C. :output terminals of rectifier 44 through :the D. JC. coil 30 of line 45 and back through line 46.. Consequently, 'by selectively Aadjusting `the potentiometer, the operator `can vary the current `through the D. C. `winding 3i) -on the reactor, control the A. C. output to rectifier f2s and consequently control the D. C. output from rectifier 23 to the generator eld winding |8.

Also located in the handle of the electrode holder, which is indicated diagrammatically by the dotted square in Figure 7, is switch i8 which controls the motor starter contactor Il. This switch is connected through lead 50 to the coil 5| of a solenoid actuated relay 52. The other end of the coil 5E emerges as a lead 53 and the circuit is completed by returning to switch t8 through lines 5d and 55 connected across the low voltage side of transformer d3. Thus, closing switch 118 will result in closing the circuit just described and energization of the solenoid relay 52.

When this relay is activated, it bridges contacts 55 which are the terminals of leads 5l and 58 connected across the high voltage side of transformer t3. Lead 58 includes solenoid coil 5B which actuates motor starting contactor Il. Obviously, the opening of switch 48 will result in the cie-activation of relay 52, breaking of the circuit contr-olling solenoid 59, and the withdrawal of starter contact I7 from operative position, thus stopping the motor I2.

Switch fit which controls the polarity reversing relay is also located in the electrode handle and makes or breaks the circuit through lead SD which includes the coil of a solenoid vSi controlling the polarity reversing relay. The other end of the coil terminates in line 52 connected to line 5ft which as previously described returns to the low voltage side of transformer t3. The circuit is completed through line 55 extending from the terminal of the low voltage side of the transformer i3 to the switch t9. Thus, closing switch iiS results in activation of solenoid 5|, causes relay 3.5 to establish a new set of con tacts and reverse the polarity of the field la.

Those skilled in the art will readily appreciate the economy achieved by energizing both the polarity reversing circuit and the motor starting circuit from the low voltage side of transformer d3. Moreover, by virtue of the arrangement shown, the number of conductors which must be extended from the control unit to the electrode holder is kept to a minimum. Lines 45, 416, 5B, 55 and til are the onlyr conductors which extend to the electrode holder other than the welding cable. It will also be observed that line 55 is connected to the terminus of potentiometer fjl through a lead 63 which also results in the reduction in the number of conductors necessary.

By way of illustration, but not by way of limitation, the following data is given to illustrate one machine constructed according to the invention:

A satisfactory system which was operated successfully from a three phase 60 cycle source in conjunction with a 300 ampere Hobart type welding generator has utilized a reactor having a winding of 620 turns on each A. C. winding and 3090 turns on the D. C. winding. These windings are coiled on a core 11/2 inches thick fabricated from laminaticns of Allegheny Ludenum E-I 19 core iron. The power utilized through this reactor was 1100 watts at minimum D. C. excitation, which was drawn from a supplying transformer having that capacity, and appr ximately zero watts at maximum D. C. excitation. The voltage drop across the reactor varied from six to ninety volts within the range limits and a rectifier appropriate to this range was supplied. Power loss through the reactor 6 was approximately 60 watts at maximum, with a 7 watt loss through the D. C. winding at minimum.

In Figure 8., an alternate circuit is shown which is also constructed in accordance with the principles of this invention. In this case however, the field iii of the current welding generator 1| is excited by a separate auxiliary generator l2. Both generators are driven through a common shaft, indicated diagrammatically by dotted lines, of a motor 13. In this case, regulation of the volt-ampere characteristics of the welding generator is achieved by control of the D. C. potential supplied to the field le of the auxiliary generator. A particular advantage arising from this arrangement is the reduction of the power requirements of the control circuit. Those skilled in the art will readily appreciate that by virtue of this arrangement the total power requirement of the welding system is supplied chiei'ly by the electric motor 73. The use of the auxiliary generator le under conditions of high flux density permits material reduction in the power requirements of the control circuit.

In this case, as in the former, the drive motor 'I3 and the control circuit for the field winding are energized by power supplied through lead lines l' from a convenient source of alternating current. For example, a three phase `60 cycle supply may be used although circuit conditions may be adapted to accommodate almost any available source of energy. In the embodiment shown, the lead lines 1B include fuses il. a main switch 'I8 and are connected through a motor starter contacter 'i9 to the drive motor '53.

Full wave rectied A. C. current hereinafter referred to as D. C. current is supplied to the field winding 'I4 of the generator '|2 through a controlled supply circuit which includes a saturable reactor and a rectifier 8|. Power is supplied to the circuit through leads 32 and 83 taken across a single phase of the lead lines 15. Lead 83 terminates in dual contacts 8&3 on one side of a polarity reversing switch 85. As those skilled in the art will understand, this switch can be selectively positioned to connect one of the contacts 84 to a contact 86 at the end of line 81 leading to one side of thegenerator field coil 14 or the other contact Sli to a contact 8B at the end of the line 89 leading to the other side of winding 14.

The other lead 82 proceeds toward the saturable reactor and branches into lines Se and 9| which proceed in parallel across the saturable reactor 80 and meet in line 92 which leads to the reversing switch 85. Contacts 93 at the end of line 92 can be selectively connected through the switch to either contacts 88 or Bt on the generator field service lines 39 and 8l respectively.

It will be observed that the connections through the saturable reactor 80 and the rectifier 8| are different in this circuit than they are through the counterpart of these elements in the circuit shown in Figure '7. In this case, lines 90 and 9| include coils 93 and 9d respectively which are wrapped around the outside legs of the reactor 80 and are arranged in parallel circuit relationship with eachother. Lines Si@ and 9| are connected to the opposite sides of rectifier 8| and by virtue of this connection are unilateral in nature permitting current to pass through them only in the direction of the arrows shown in the rectier connection in each line. Hence, lines 90 and 9| Valternately carry half `wave rectied currents and the current supplied f coils; 93 and 94 on the outer legs of the reactor, the current owing rthrough these coils serves 'to expedite the saturation of the core rin a step process. In effect, the current passing through the coils 93 and 94 in tending to saturate the core, progressively diminishes the core impedance and consequentlyv permits larger currents to flow in the windings 93 and 9,4 until saturationA or near saturation. is reached. Consequently, lesspower is required in the circuit to saturate the rcore because the D. C. in coil 95 is supplemented by the D. C. components in coils 93 and Q4. I t will be observed however, that ythe ulti'- y f mate control is achieved by regulation of the direct current passing through the central winding 95.

f tentiorneter-All. The numbers t?, and 4s refer.

The D. C; control circuit for the middle coil* 95 ofthe saturable reactorvv is isubstantially similarH to the corresponding circuit of the system shown rin Figure 7. Power is taken from the source lines 16 through' leads 98 and 99 and fed tothel primaryofy a transformer |08. The secondary of the transformer is connected through leads I and |02A to the A. C. terminals of a rectifier |03. f This rectifier feedsy D. Cv. current through a circuit which can be traced through f line |04, line 96 to one end of coil Q5, line al connected to the other` end of coil 95 adjustable potentiometer |05' and return lin-e |06; .adjusting the. potentiometer will result variance ,or theY resistance in, tho circuit and the consequent control of the D. C. currentl passing throughA coil Q5, Potohtiomoter |05; is, or cmlrso` located in the. handle oi an electrode holder.

The motor` Startins oohtaotor 7:9 and;Y the polarity reversing switch 8,5 are controlled by switches |01' and; |08 respectively which, are also located in the. electrodeV holder handle. Since the control circuits which include thesefswitches are practically identical to the control circuits of the system shown in Figure 7; a detailed description will not be made. In general, however, tho polarity reversi-hs' switch control circuit which includes switch H38V comprises leads |019 andv ||0 connected across the low voltage side oftransioriner |00., Lead Ill); proceeds through switch` |08 and; thence to solenoid which actuates the polarity reversing switch; Lead `hll proceeds directly t9 'the' otherl side of the solenoid coil.

The solenoid of the motor star-ter contactor "s3: iS.; connected across the high voltage side of transformer |00 through lines. I l2 and ||3:. Line |:|,3 passes solenoid actuated relay H4. The coil of this relay is actuated by a circuit which may be traced'` through conductor H5 leading to Yline |09: to one side of the secondary or transformer |100 and lead I I6 which passes'throughL switch |101 and returns the current to the other` side of the secondary of transformer |00, through lead 0. Y l

A typical electrodo holder, which. iholudosjthe oohtrol moans adapted for. use( with tho,- oroiiits shown in Figures 7v and 8,A` is shown in Figures 1 to 6- The electrode holder showin; i'soi- ,tho

type, suitable in,y general for commercial use4 and 'those skilled in the artfwill understand that it is representative only. TheY control means of this. invention can be adapted to almost any commercial type ofl holder. The holder shown comprises a tubular handle membery |20V which houses4 the terminus oi the welding cable IZI- Projecting from they forward end of the handle are a pair of spring-urged jaws |22 which are adapted toy clamp yan electrode between them. The jaws are actuated by a manually operated lever |23 rwhich drives anl arm |24 into and out of spreading engagement with the jaws.

The control means. ci this invention are contained in a tubular housing indicated generally at |25 and attached to. the cable end ci the holder handle. Mounted inan exposed position ron theyhousing are the switches d8 and d, which control the motori starter contacter and the polarity reversing vrelay respectively, and the poin this instance, tothe controls indicated diagrammatically in Figure '1, but/it will be apparent that these controls can he the controlsv |95, |01 and |08 or the circuit' of Figure 8. |25. comprises a tubular side wall |26 fabricated 'from ar suitable insulating material and which is attached to a collar |2l ttedy around the end o thehandle |22. The end oi an insulated sleeve 23` is slip-litted into the interior'foi 'the member 20 and is adapted to pass the welding cable |21.

The sleeve collar and the outer wall are detachably fastened to thcfelectrode handle |29 by means of screws |29. A hub i3d is rotatably f mounted between the side wall |25 andI the f sleeve 32a and is freewto turn relative to and between these members.y yThe hub. is prevented from being disconnected by means of a stoppin |3i screwed into the sidel wall |25 jecting inwardly into. an.y annular groove |324 in the hub |39.

A preferred form ci potentiometer, indicated at di' in Figure, 1, is shown in detail in lrigures 4;, 5 and 6. Generally, it comprises a resistance coil l3-3 which is wrapped around the. outside Y ol sleeve t28. A band conductor |34 which is in the form of a dat copper strip circles the coil and is insulated trom it by a non-conductive spacer 35. As best seen in Figurel 2, leads |36 23T (corresponding to leads E3 and i6 in Fig-ure 7) are connectedl to the opposite ends of the coil through straps ld-43S while the conductor band |34 has its ownlead 39 (corresponding to lead in Figure 7) which is iastened to the overlapping ends of the band by t means of a screw Hill.`

Contact betweenthe coil and the band is achieved through a contact ball Il which is urged into bridging position between the band edge and the exposed side M2 of the. coil. by means of a spring. L43. seated in the hub, ist. Rotation ci the hub will cause the bail to roll along the track formed between the band and the resistance coil and thus vary the resistance interposed in the Circuit. Preferably, the outside of the hub is provided with graduated indicia |44 which may be chosen, to represent volts, amperes or arbitrary units referable to a voltampere chart.

The operator is prevented from inadvertently turningthe` hub. too far and running the ball off the tracl by. shoulders M5, Figure a, formed at the ends of groove |32 and which abut the stop pin, |3,l. It will he apparent that the oporator can set the potentiometer to any predetermined The housing and proresistance value by rotating the hub until the graduations come into alignment with alignment marks scribed on the outside of the side wall |26 and thus he can conveniently and easily regulate the generator characteristics by adjustment of the potentiometer.

The construction of the motor contactor control switch d8 and the polarity reversing relay switch te is shown in Figures 2, 3, 4, and 5. Since they are practically identical in construction they will be described together. Each comprises a finger manipulated throw-block |45 which can be slid longitudinally along the side wall to open or shut position. Each block is rigidly connected to a slidable insulated block la? on the inside of the tubular side wall |25 through a slot block |58. Movement of the outside block |46 in each instance will cause corresponding movement of the inside block lll?.

Each block |51 carries on its inside surface a metallic conductor plate |55 provided with detent cavities B. Fixed on the inside of the wall adjacent the path of movement of blocks |47 are insulated mounting pads |5| for a pair of spaced spring contactors |52 and |53. One end of each of the contactors |52 is connected to one of the leads 55 and 53 of the respective control circuits while one end of spring contactor |53 of switch 48 is connected to conductor 55 leading to the control circuit and to another conductor |55 leading to one end of contacter 55 of switch 49. The other end of each contacter extends laterally into the path of the shiftable plates |49. This end of each spring contacter is provided with a rounded portion |55 which rides upon the block surface and when properly positioned engages the detent cavitiesi563.

Hence, when either of the switches d3 or 49 is withdrawn toward the rear of the electrode handle, which is the position shown in full lines in Figures 1 and 3, the conductor plates its do not bridge the space between the portions 54 on the respective spring contactors |52 and the circuit is open. However, when the blocks are shifted forwardly to the positions shown in Figures 1 and 3, the conductors establish contact between the two rounded portions |55 on the respective spring contactors and the circuitl is closed. It will be observed that the switch blocks are sustained against accidental drifting by engagement of the rounded portions i5@ in the detent cavities |55 when the switch is in either opened or closed position.

A particularly novel feature of this invention resides in the construction of the polarity reversing switch This switch is so constructed that it can only be thrown when the potentiometer is set at zero. In other words, the operator must set the potentiometer at the zero position so that all added resistance is withdrawn from the circuit before he can reverse the polarity of the generator field winding. The advantage of this provision is that it prevents the relay control from being thrown accidentally and inadvertently switching the generator iield current during the welding operation. Moreover, it also insures the rapid reverse of the generator eld. If the polarity reversing switch could be thrown when resistance is in the control circuit a static magnetic field established by the generator winding may be maintained without reversing for an indefinite period of time. However, by virtue of this provision reversing can only take place when no resistance is in the circuit and consequently the igenerator leld reverses immediately.

In order to accomplish this purpose, the polarity reversing switch is provided with an angulated extension strip |55 which has a laterally projecting stop ange 51. When the switch is in opened position, this iiange rides in groove |32 and is maintained therein by spaced annular shoulders |58 and |59. 'I'he foot is dimensioned so that it can only pass shoulder |58 when it is aligned With a slot |50 formed in shoulderl |58. This alignment is only achieved when the hub is rotated so that the potentiometer is set to zero position.

When the polarity reversing switch is thrown to closed position, the stop flange has passed through the slot |551 and rides the other surface of shoulder |53. As shown in Figure 5, this shoulder stops the flange and prevents the switch from being thrown to open position unless the potentiometer is set to zero and slot it aligned with the flange. It will be observed that adjustment of the potentiometer hub is possible whether the switch c is open or closed.

Having described my invention, I claim:

1. A system for remotely controlling the output of a D. C. welding generator supplying current to a pair of welding electrodes by adjustment of the generator eld excitation, said system cornprising; a circuit for supplying rectified A. C. energy to the generator field from a source of A. C., said supply circuit including a rectifier and a saturable reactor for controlling the A. C. input from said source to said rectifier, and a control circuit including a control winding on said saturahle reactor and a variable resistance installed in the handle of one of the electrode holders whereby variation of said resistance results in control of the energy supply to said control winding, adjustment of the A. C. input to said rectifier and consequent adjustment of the rectified A. C. input to said generator eld.

2. A system for remotely controlling the output of a D. C. welding generator supplying current to a pair of welding electrodes comprising; means for supplying rectified alternating current to provide the energy for exciting the eld winding of the generator, said means including a rectifier and a saturable reactor for controlling the input from an alternating current source to the rectiiier, and a control circuit including a control winding on said saturable reactor and a variable resistance installed in the handle of one of the electrode holders whereby variation of said resistance results in control of the energy supply to said control Winding, control of the A. C. input to said rectier and consequent adjustment of the energization of said generator eld.

3. In a control device for welding generators of the type including a supply circuit for supplying exciting energy to the iield of said generator, said supply circuit including a saturable reactor for varying the output of said supply circuit, a control circuit for varying the saturation of said reactor, and a polarity reversing circuit for said generator, a remote control attachment adapted to be built into the handle of an electrode holder comprising; a switch controlling the polarity reversing circuit and a variable potentiometer controlling the energy supplied through said control circuit, said switch having stop means in cooperative engagement with said potentiometer to prevent the switch from being thrown except when said potentiometer is adjusted to zero resistance position.

4. A control device for governing the output vcharacteristics of a direct current welding gener- 

